1. Field of the Invention
The present invention generally relates to an apparatus and associated method for supporting sub-assembly components during their construction in a manufacturing process. The present invention more particularly relates to an apparatus and associated method for supporting sub-assembly portions of a vacuum interrupter during their manufacture.
2. Description of the Prior Art
Vacuum interrupters are typically used to interrupt medium and high voltage AC currents. The interrupters include a generally cylindrical vacuum envelope surrounding a pair of coaxially aligned separable contact assemblies having opposing contact surfaces. The contact surfaces abut one another in a closed circuit position and are separated to open the circuit. Each electrode assembly is connected to a current carrying terminal post extending outside the vacuum envelope and connecting to an AC circuit. The subject matter of U.S. Pat. Nos. 5,777,287 and 5,793,008 provide examples of conventional vacuum interrupter technology.
Conventional support construction applies to sub-assemblies for both (1) a stationary vacuum interrupter electrode and its end plate, and (2) a moveable vacuum interrupter electrode and associated components supported by the electrode, such as the bellows and bellows shield. This conventional construction requires that a structural support step or ledge be machined into the electrode body to provide a stable location onto which parts may be stacked for further production processing, such as brazing.
The material removed by machining this ledge produces an electrode with a smaller cross-sectional area. This reduction in cross-sectional area causes the current density of the electrode to increase during operation. An increase in current density unfavorably results in increased heat generated by current passing through the electrode. As the current density in the electrode decreases, however, the heat generated by the electrode will decrease as well. By increasing the cross-sectional area of the electrode, or by reducing the amount of material machined from the electrode, it becomes possible to increase the amount of continuous current passed through the electrode without exceeding operational temperature limits for the electrode. In addition, current density is a function of the square of the cross-sectional area of the electrode. As a result, a reduction in the amount of material removed from the electrode can decrease the current carrying capacity of the electrode as a function of a squared variable, namely the cross-sectional area of the electrode.
To form the ledge or step in the electrode, a significant portion of material must be machined from the electrode on an automatic or manual lathe and discarded. In addition, conventional practice for production of a vacuum interrupter electrode sub-assembly necessitates providing a staking ring mechanically engaging the electrode to support and maintain the positioning of components, such as the bellows and bellows shield, which are supported by the electrode. The staking ring is specifically employed to prepare the electrode sub-assembly and its associated components for a subsequent brazing operation.
In spite of the foregoing methods for constructing stationary and moveable electrode sub-assemblies, there remains a real and substantial need for an apparatus and method of construction to minimize the problems associated with conventional vacuum interrupter manufacturing practices.